Studying The Flow Of Magnetism On The Sun

August 28, 2013

Image Caption: Observations by the Helioseismic and Magnetic Imager on NASA's Solar Dynamics Observatory show a two-level system of circulation inside the sun. Such circulation is connected to the flip of the sun's north and south magnetic poles that occurs approximately every 11 years. Credit: Stanford

The SDO has an instrument onboard known as the Helioseismic and Magnetic Imager (HMI). This instrument has allowed scientists to observe a two-level system of circulation within the sun. Understanding this circulation will be especially important in the coming months as the sun’s magnetic poles flip.

The sun is full of activity, ranging from dark blemishes called sunspots to strong, loopy explosions called coronal mass ejections. This activity is all powered by the sun’s ever-changing magnetic current inside it, known as the dynamo. This system flips about every 11 years, with the north and south magnetic poles switching places. The activity is an integral part of the solar activity, and marks the main event known as a solar maximum.

Scientists writing in the Astrophysical Journal Letters say they’ve found that the material inside the sun shows a double layer of circulation, with two cycles on top of each other.

“For decades people have known that the solar cycle depends on the poleward flow or material, changing the magnetic fields from one cycle to the next,” said Philip Scherrer, principal investigator for HMI at Stanford University in Stanford, Calif. “We mapped out what we believed to be the flow pattern in the 1990s, but the results didn’t quite make sense.”

The 1990s technique, called helioseismology, makes use of the fact that waves course across the sun, back and forth, oscillating with about a five minute period. Scientists can monitor oscillations seen at the surface of the sun in order to understand the material through which the waves traveled. These observations helped show scientists how material inside the sun rotates from east to west.

“Scientists have used this assumption to describe the solar dynamo,” said Junwei Zhao, a helioseismologist at Stanford University in Stanford, Calif., who is the first author on the paper. “And now we have found that it isn’t right. The flow patterns we have found are sharply different.”

Astronomers used two years worth of data taken by HMI and compared the helioseismology results measured at four different heights within the sun’s surface. They found that these results were not consistent with what the normal convention would expect. Instead, the team proposed a way to make these sets of measurements agree with each other.

The team found that the equatorward flow inside the sun isn’t at the bottom, but instead the material seeps back toward the equator through the middle of the convection layer.

“This has important consequences for modeling the solar dynamo,” said Zhao. “We hope our results on the sun’s interior flow will provide a new opportunity to study the generation of solar magnetism and solar cycles.”

The team provided their new map of the sun’s interior to scientists who simulate the dynamo. The next steps for these scientists is to see whether the new models fit with observations seen on the sun and how they may improve the ability to understand magnetism on the sun.